Fluid pumping method and apparatus



FLUID PUIPIHG METHOD AND APPARATUS FilQd 569i. 9, 1968 lllllllllllllllll llll/ INVENTOR. Thomas E. Roberts, Jr.

ATTORNEYS United States Patent US. Cl. 209-170 7 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for delivering fluid (e.g. water) to a high pressure reservoir and for releasing fluid from the reservoir to a lower pressure level, all with a relatively small amount of power consumption. Power is supplied to a fluid pump to cause the pump to deliver fluid to the reservoir under pressure. During operation of this pump a stream of fluid is caused to flow from the reservoir to a lower pressure level with release of useful energy. This energy is utilized to provide a part of the power for driving the pump. In a particular embodiment, the invention is incorporated in a flotation method and apparatus, with air being dispersed into liquid eflluent while in the pressure reservoir, and with the discharging liquid being routed to flotation separating equipment.

BACKGROUND OF THE INVENTION In certain industrial methods and apparatus a liquid (e.g. water, waste or processing liquors, etc.) is pumped to a pressure reservoir and simultaneously withdrawn from the reservoir to a lower pressure level. The body of liquid within the reservoir may be subjected to various treatments such as absorption of air or other gas, blending with additives or reaction with chemical agents. Particular reference can be made to flotation methods and apparatus where it is common to pump water or effluent to a closed pressure reservoir where it is caused to absorb air. The stream of water containing absorbed air is withdrawn from the reservoir through a throttling valve after it is delivered to flotation separating equipment. One problem with such methods and apparatus is the power consumption required to drive the pump which delivers the liquid to the pressure reservoir. This power consumption adds substantially to the over-all cost of operation.

SUMMARY OF THE INVENTION This invention relates generally to methods and apparatus of pumping fluid into a pressure reservoir and for releasing fluid from the reservoir to a lower pressure level. In one embodiment the invention is incorporated in a flotation method and apparatus, wherein eflluent is contacted with air in the pressure vessel.

In general it is an object of the invention to provide a method and apparatus of the above character which makes possible a substantial saving in power consumption.

Another object of the invention is to provide a method and apparatus of the above character which makes use of the energy of liquid discharging from the pressure vessel for supplying a substantial part of the power required to drive the pump.

Another object of the invention is to provide an improved flotation method and apparatus characterized by low power consumption for circulating efliuent through a pressure reservoir.

Additional objects and features of the invention would appear from the following description in which the preferred embodiment has been set forth in detail.

In the present method power is supplied to drive a pump which in turn delivers fluid to a pressure reservoir. Simultaneously with supplying liquid to the reservoir, a

3,501,000 Patented Mar. 17, 1970 stream of fluid is caused to flow from the reservoir to a lower pressure level, with release of useful energy. This useful energy is utilized to provide a part of the power for driving the pump. The apparatus includes a fluid pump and driving motor for delivering the fluid to the pressure reservoir, and a fluid motor through which the stream of liquid being withdrawn from the reservoir is caused to pass. The motor is effectively coupled to supply power to the pump motor system.

BRIEF DESCRIPTION OF THE DRAWING The single figure of the drawing schematically illustrates flotation apparatus incorporating the present invention.

DETAILED DESCRIPTION OF THE DRAWING The apparatus shown in the drawing consists of a liquid pump 10 which delivers liquid to the closed pressure reservoir 11. The pump is indicated as being driven by the motor 12, which may be electric. A fluid motor 13 has its inlet side connected to the pressure reservoir 11 and its discharge side connected by line 14 to the flotation unit 16. As schematically indicated fluid motor 13 is connected into the drive means which connects pump 10 with motor 12. By way of example the respective drive shafts 10a, 12a and 13a of pump 10, motor 12, and motor 13, may all be mechanically coupled together. To enable control of the relative speeds adjustable or variable ratio coupling means C can be connected between the motor 13 and pump 10. The drive ratio between the pump 10 and the motor 13 is normally set so that for the desired operating pressure in reservoir 11 the pump 10 supplies slightly more liquid than the hydraulic motor 13 passes. The excess liquid goes through a pressure relief valve 17 which is set whereby the reservoir pressure is always the set pressure of the relief valve.

Assuming use of the invention in flotation separation apparatus, the closed reservoir 11 has its lower end connected to a gas supply line 18, which can supply air or other gases at a pressure sufficient to cause it to be dispersed in the liquid within the tank. The rate of gas flow into the reservoir is shown being controlled by flow regulator valve 19. The tank can be provided with an inner baffle 20, thereby somewhat isolating the zone into which the gas is introduced, from the zone which connects with the motor 13. The space above the liquid in tank 11 is occupied by compressed air or other gas, depending upon the particular gas introduced through line 18. The liquid level in reservoir 11 may be controlled by use of the float controller 19a which is schematically shown connected to flow regmlator 19 so as to control the gas flowing from supply line 18.

The pump 10 can be of the centrifugal or displacement types, depending upon conditions and requirements. Likewise the fluid motor 13 can be a hydromotor of the turbine or displacement types.

The flotation unit 16 shown consists of a tank 22 which receives influent through line 23 and is provided with an endless belt type skimmer 24 for discharging a separated fraction over launder 26. However, separated material is acted upon by rake 27 and is discharged through line 28.

When the apparatus described above is in operation, a liquid influent is supplied through line 23 to the tank 22 of the flotation unit 16, and liquid eflluent discharges continuously through line 29, with a portion of this eflluent being supplied to the intake side of the pump 10. Pump 10 and motor 13 operate continuously and simultaneously. A substantial pressure is maintained within the pressure reservoir 11, which again may vary with different conditions and requirements. By way of exampie, in flotation apparatus this pressure may be on the order of 80 p.s.i. as set by adjustment of valve 17. Liquid being withdrawn from the reservoir 11 serves to drive the motor 13, and the liquid discharging from this motor is substantially at atmospheric pressure. The flow rate through the motor 13 can be adjusted by proper choice of the drive ratio between motor 13 and pump 10.

Flow of liquid through the motor 13 with a drop in pressure to substantially atmospheric, provides considerable useful energy. This energy or power is utilized by applying it to the pump Ill-motor 12 system, thus effectively reducing the power requirements of the motor 12 and causing a corresponding saving in electrical power consumption.

When the pump 10, reservoir 11 and motor 13 are incorporated in flotation apparatus as shown in the drawing, retention of liquid in the pressure reservoir 11 in contact with other gas introduced by way of line 18 and dispersed in the form of small bubbles, causes a certain amount of gas to be absorbed in the liquid. Some of this gas is released in the form of fine bubbles as the liquid passes through the motor 13 with reduction in pressure. In the flotation unit, rising gas bubbles, attach themselves to solids suspended in the eflluent, thus causing such solids to rise to the surface for removal by the skimmer. Heavier solids present settle to the bottom of the tank for removal through pipe 28.

The following example will suffice to show the savings which can be ellected in a particular instance. It is assumed that the flow through the appaartus of influent and efiluent, is one million gallons of water per day. If a conventional throttling were substituted for motor 13 and regulating valve 17, according to prior practice, the circulation of liquid through the reservoir 11 in a typical instance may be of the order of three million gallons per day. For handling this amount of liquid the electric motor 12 would normally have a capacity of 150 horsepower. The cost of the electrical power to operate this motor, based on one cent per kilowatt hour, would be $30.00 per day, or in other Words $30.00 per million gallons flowthrough. Assuming typical efliciencies for the pump 10, electric motor 12, fluid motor 13, the electrical motor with the present invention requires a capacity of only 60 horsepower, and the cost of power consumption is $12.00 per day, or $12.00 per one million gallons flowthrough. This means a saving of $18.00 per day for elec tric power. In general, it may be stated that the power saving made possible by this invention may range from about 30% to 60% of the power required under comparable conditions where a throttling valve is substituted for motor 13.

With respect to the flotation method and apparatus, particular reference can be made to hydrous influents carrying some suspended solids, such as clarified efliuent from an activated sludge sewage disposal plant which consists of Water with a minimum amount of suspended solids. However, the method and apparatus is applicable to a wide variety of industrial liquors where solids present are susceptible to flotation by attachment to gas bubbles as previously described.

What is claimed is:

1. A method for maintaining fluid in an enclosed high pressure reservoir at minimum power consumption while permitting fluid flow therethrough comprising the steps of supplying power to drive an inlet fluid pump, said pump supplying fluid from a source into said reservoir at high pressure, maintaining said pressure while releasing fluid at high pressure from the enclosed reservoir to a substantially lower pressure, driving a motor with said released fluid to reclaim useful energy, supplying the energy reclaimed by said motor to the inlet pump and controlling the rate at which said fluid is released to maintain a substantially constant pressure in the reservoir.

2. The method of claim 1 wherein the reclaimed energy is transmitted as mechanical power.

3. A method for removing suspended solids in a flotation unit comprising the steps of supplying power to drive a liquid pump, causing the pump to deliver liquid to an enclosed high pressure reservoir against the pressure therein, injecting gas into the liquid whereby the gas is absorbed, releasing the fluid and absorbed gas from the reservoir to a lower pressure in a flotation unit, driving a motor with said released fluid and gas to reclaim useful energy, supplying the energy reclaimed by said motor to the inlet pump, releasing the absorbed gas from the liquid at the lower pressure so that small bubbles are formed, supplying the liquid and gas bubbles to the flotation unit, attaching the suspended solids to the gas bubbles which rise to the surface of the flotation unit and skimming the floated solids from the surface of the unit.

4. The method of claim 3 including the step of maintaining the input flow greater than the flow released from the pressure reservoir.

5. The method of claim 3 including the steps of maintaining the input flow greater than the flow released from the pressure reservoir, and controlling the rate at which liquid is released to maintain a substantially constant pressure in the reservoir.

6. A flotation system comprising a closed high pressure reservoir, a pump connected thereto to deliver liquid under pressure, means for introducing gas into the reservoir whereby the liquid is caused to absorb at least some of the gas, a fluid motor adapted to be driven by liquid under pressure, means for supplying said liquid under pressure from the reservoir to the motor to drive the motor and deliver the liquid to a flotation unit at a lower pressure, means utilizing power from the fluid motor for assisting the driving of the pump and a skimmer to remove suspended solids from the surface of the flotation unit, said suspended solids having attached to gas bubbles formed by the absorbed gas when released to a lower pressure.

7. Apparatus as in claim 6 including additional regulator bypass means for permitting discharge of liquid from the reservoir to the flotation unit when the reservoir pressure reaches a predetermined value.

References Cited UNITED STATES PATENTS 224,299 2/ 1880 Leininger 60-55 255,312 3/1882 Maxim 6055 X 627,925 6/1899 Hagen 6055 776,724 12/1904 Caverno. 1,002,676 9/ 1911 Gray. 1,167,835 1/1916 Norris 209- 1,618,258 .2/1927 Young. 3,100,310 8/1963 Meyer 26l1l5 3,286,844 11/ 1966 Juell 209170 X FOREIGN PATENTS 229,211 2/ 1925 Great Britain.

FRANK W. LUTTER, Primary Examiner US. Cl. X.R. 60-55; 1036 

